1. Field of the Invention
The invention relates to a rolling bearing.
2. Description of Related Art
If an amount of a liquid lubricant (mainly, lubricating oil) supplied to a rolling bearing becomes excessively large, stirring resistance of the lubricant during the rotation of the bearing increases, and thus it becomes difficult to achieve lower torque. In order to suppress an increase in the stirring resistance of the lubricating oil, for example, a rolling bearing described in Japanese Patent Application Publication No. 2012-87864 (JP 2012-87864 A) has been used. According to JP 2012-87864 A, an inner ring and an outer ring are provided with respective bearing ring extension portions extending in an axial direction, and an oil supply and discharge mechanism that supplies lubricating oil, which also serves as a bearing cooling medium, into a bearing and that discharges the lubricating oil out of the bearing is formed in the bearing ring extension portions. Further, a technique in which a solid lubricant instead of a liquid lubricant is applied on a raceway surface for balls in a bearing has been employed in order to suppress stirring resistance.
In the rolling bearing described in JP 2012-87864 A, due to the structure in which the inner ring and the outer ring are provided with the respective bearing ring extension portions extending in the axial direction, each of the weight and the axial length of the rolling bearing increases by an amount corresponding to the bearing ring extension portions, resulting in an increase in the size of the rolling bearing. On the other hand, in the case where the solid lubricant is used instead of the liquid lubricant, there are problems that, for example, the solid lubricant is inferior in heat dissipation characteristics to the liquid lubricant and abrasion powder may adversely affect lubrication.